The singular purpose of ensiling forages is to preserve it in a moderately moist environment after it’s been harvested – especially those crops that are seasonal, such as corn. The objective of ensiling forages is to preserve and recover organic dry matter, while retaining nutritional value and palatability. In the current economic environment of escalating grain prices, high-quality silages will help increase feeding efficiencies.

The process of ensiling forages – whether it be corn, grasses or legumes – is not complicated. Once a crop is chopped and packed, bacteria use the natural sugars and starches to initiate a fermentation process that uses up the available oxygen, converting part of those sugars and starches into a number of different acids that preserve the organic matter.

Lactic acid is the strongest and most abundant acid produced in an ideal fermentation, and the presence of lactic acid at a level of 6 to 8 percent of the total dry matter is optimum. Acetic acid is also present in silage but at lower levels than lactic acid.

During fermentation much of the acetic acid will be converted to lactic acid and a final ratio of 3-to-1 (lactic-to-acetic acid) is desirable. Acetic acid at levels of more than 4 percent of the total dry matter indicates there was a slower fermentation, and if acetic levels are too high you may notice the familiar smell of vinegar in the silage. The more quickly lactic acid can be produced the less chance there will be for dry matter loss or the formation of harmful organisms such as yeasts and mold.

The presence of higher levels of acetic acid in corn silage, in and of itself, is not necessarily a bad thing. What it tells us, though, is that you’ve probably lost some dry matter due to excessive respiration and the formation of other volatile end products such as alcohol.

Butyric and propionic acids may also be present in the silage. However, these two acids should never be found in anything greater that trace amounts. The presence of either of these two acids indicates that very poor fermentation has occurred during the ensiling process. Butyric acid can be especially troublesome since it can be accompanied by high levels of clostridium in the silage.

High levels of butyric acid quite often result from the silage being put up too wet which prevents the pH from dropping fast enough. It can also be present due to poor grain development in the crop and, consequently, not enough starch to adequately support proper fermentation. Butyric acid tends to be a greater problem in grass and legume silages.

Once a plant has been harvested, it immediately begins to decay. This decaying process is supported and encouraged by the presence of oxygen and bacteria. To keep decomposition (rotting) to a minimum, oxygen must be eliminated from the storage environment. We do this, of course, by stacking the feed on a big pile, pressing and packing it down with a tractor or bagger, if it’s being put in a horizontal bunker or storage bag; or by its own weight if it’s going into an upright silo. When the air supply is depleted the entire fermentation process shuts down, the level of acidity stabilizes (pH) and the crop will remain in a stable state of preservation for many months. A pH of about 4 is where a well-fermented silage should end up.

The single-most critical factor affecting silage quality is the moisture level at which it goes up. Trials have shown repeatedly that the moisture level at the time of harvesting of corn, grass and legume silages has the greatest influence on a good fermentation and how much dry matter was recovered. Analysis results summarized by the Cumberland Valley Analytical Service in Maugansville, Maryland (CVAS) has shown lactic acid levels in corn silage tend to be the highest in dry matter ranges from 26 to 32 percent. Silage that was wetter than 26 percent showed higher levels of acetic acid relative to the lactic acid levels, which indicates that the fermentation process does not proceed as rapidly once the dry matter dropped below 26 percent. Corn silage that is dryer than 36 percent again showed a drop in lactic acid levels as well as a drop in total acids, indicating that there is poorer fermentation in dryer corn silage.

Most of you have put up some grass or legume silage already this season, and you know how difficult making good haylage can be. Hay crops have only a fraction of the soluble carbohydrates that corn has, making a good fermentation more difficult. CVAS data has shown that the highest lactic acid levels in grass and legume crop silage occur between 32 and 40 percent dry matter. As with corn silage, the acetic acid in haylage increases as the moisture increases, indicating a slower fermentation. Wetter haylage crops will also produce more butyric acid which can adversely affect the quality and palatability of the silage.

A second factor that will have a large negative impact on silage quality is the rate at which silages are packed and how quickly the pile is sealed from the air. It’s imperative that the air is squeezed out of the feed as quickly as possible so that the pile will stop cooking. Excessive heat in a pile of silage will alter the proteins in the feed. In the case of grasses and legumes where the crop is being harvested for maximum protein, rapid fermentation and stabilization will ensure undamaged protein. Whether you’re putting the silage up in a silo or packing it in a pile or bag, get the silage packed as quickly as possible, use a silage preservative and when you’re finished get it covered as soon as possible. A well-packed pile of corn silage should have a density of about 45 to 50 pounds per cubic foot in the pile (45 - 50 lbs/ft3).

Serious consideration should be given to using a microbial inoculant on your silage to aid in the fermentation and preservation of the silage dry matter. Significant research has shown that the dry matter recovery in a pile of silage is well worth the dollars invested in an inoculant. There are a number of inoculants on the market, both dry and liquid, so you should consult with your nutritionist or extension agent in determining the product that would be best for your crop.

Mechanical processing has been used on corn crops for many years. A dry stand of corn will benefit the greatest from a processor. Processing corn silage improves starch and fiber digestion and allows for good packing in silos even with a longer length of particle chop. Care needs to be taken, however, in using processors on stands that are too wet since particle size can be made too small, affecting rumen function.

The type of silage storage environment needs to be well thought out. Traditionally, upright silos have worked well for smaller herds that require housing. Larger herds can make good use of horizontal piles and pits. However, these require a much more extensive level of management both in terms of covering and protection from weather and the amount of silage exposure as the pile is fed out.

Piles should be sized so that the face can be removed to a depth of 6 inches or more, every day, if possible. Once silage is re-exposed to air, it will experience a secondary fermentation and the quality will rapidly decrease. A mechanical facer does a good job of managing the front of large silage piles.

A full analysis of the silage for dry matter, fermentation acids, crude protein, soluble protein, neutral detergent fiber, starch and lignin and fiber digestibility should be done to determine the true nutritional value of the silage. Macrominerals including potassium, chlorine, sulfur and sodium should also be analyzed to aid in the formulation of transition cow rations.

Dairy farmers who grow their own forages have a sizable investment in that crop by the time it’s ready for harvest. Even if the weather doesn’t always cooperate when it comes to harvesting, it’s still worthwhile to do the best job possible in ensiling. Dry matter and nutrient loss can be significant if silages are not put up correctly. Proper management of the crucial ensiling process will aid in ensuring a high-quality, highly palatable forage that will feed your cows for another season. PD

John Hibma
Nutritionist
hibmajl@cox.net

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